1. Field of the Invention
The present invention relates to improvements in the circuit arrangements for the control of digital signal transmission, particularly PCM-signals, between stations of a time division multiplex telecommunication system.
2. Description of the Prior Art
Several systems of the above described type have been proposed and described in the prior art. One of the prior art systems is described in published German Application De-OS No. 20 64 530. The major disadvantage of this known circuit arrangement is that a separate multiplex line is required for the traffic between stations of two different station groups and that the amplifiers that must be added between the trunks and the multiplex lines must have different amplification factors. Another disadvantage is that, because of the serial signal transfer over the trunks as well as the multiplex lines, only a relatively small number of subscriber stations can be included in a connection.
A circuit arrangement for the conversion of analog signals, especially those formed by PAM-signals, into PCM-signals, is already known and is described in U.S. Pat. No. 3,984,829. Therein, the signal bits, forming the individual PAM-signals, are received and transmitted in parallel via a corresponding number of individual lines. The circuit arrangement in question thus represents a so-called codec, which connects a subscriber station that transmits or receives analog signals with an exchange. But nothing is known in this connection regarding the structure of a circuit arrangement to control the transmission of digital signals between stations of a time division multiplex telecommunication system and particularly a PCM-time division multiplex telecommunication system.
A circuit arrangement for controlling the transmission of digital signals, particularly PCM-signals, between subscriber stations of a time division multiplex telecommunication system, particularly PCM-time division multiplex telecommunication system and a four-wire mode operated two-wire multiplex line is described in published German Application De-OS No. 27 24 096. Therein, each respective subscriber station is allocated one transmission pulse for a signal transmission and a chronologically separate reception pulse for a signal reception on the respective multiplex line. Each subscriber station is connected with the input of a transmission memory and the output of a reception memory via a coding-decoding arrangement, particularly one operating on the iterative principle, i.e., a codec. A decentralized holding set circuit is associated to the respective subscriber station for the control of signal storage in the reception memory and for the control of the reading out of signals from the transmission memory. In this decentralized aggregate halt circuit the counter positions of a cyclically operated counter--which can be set to one of the number of counter positions that corresponds to the number of the pulses available on the two-wire multiplex line for a signal transmission during the duration of each of the relevant pulse frames on the two-wire multiplex line--are compared with a reception pulse address that corresponds to the reception impulse serving to control the associated reception memory, and with a transmission pulse address that corresponds to the transmission pulse serving to control the associated transmission memory. When agreement is detected between one counter position of the counter and the reception pulse address and another counter position of the counter and the transmission pulse address, a corresponding control signal is transmitted by the respective decentralized holding set circuit to control the storage of a signal in the reception memory, or to control the reading out of a signal from the transmission memory of the associated subscriber station. Since in this familiar circuit arrangement the transmission memory associated to the respective subscriber station and the reception memory associated to the respective subscriber station merely serve as buffer memories for a serial signal bit transmission, also an exchange arrangement equipped with such subscriber stations has the disadvantage that it only provides for a relatively small number of connections altogether. At this point it should be noted that the possibility does exist to connect multiplex lines associated to the individual station groups or subscriber station groups via a space coupling arrangement, in order to raise the number of connections that can be established or can exist at the same time. But this entails an often undesirable, additional circuit complexity.
Another telecommunication system for a multi-branched junction network operating on the time division multiplex principle is described in U.S. Pat. No. 3,846,587. Therein, individual subscriber stations are connected by one transmission and one return line each, along the network branches, on the multiple access principle. In this familiar telecommunication system a synchronizing word generator can periodically transmit a synchronizing word from a central location of the network in a basically familiar manner, in order to form a time frame. At the extreme ends of the telecommunication system, the synchronizing word can be transferred from the transmission line to the return line. At each subscriber station the interval between two synchronization words can be divided into equal time slots by a bit cycle and time slot cycle unit in a basically familiar manner. The information emanating from a transmitting subscriber station can thus be transmitted as a block of information in one time slot. The address of the selected subscriber can be placed ahead of each information block to be transmitted, and by use of an address evaluation unit each subscriber station can ascertain whether the own address is contained in the time slots of one of the connected lines, with an address and a block of information completely filling a time slot. A disadvantage of this familiar telecommunication system is that, in spite of the use of closed circuit multiplex lines, only a relatively small number of subscriber stations can be included in connections.